1. Field of the Invention
The present invention relates to a novel, optically active phenyl pyrimidine compound and a liquid crystal composition comprising the optically active phenyl pyrimidine compound.
In this instant specification, by the term "liquid crystalline substance of material" is meant not only a substance showing a liquid crystalline phase but also a substance or material which is valuable as a constituent of a liquid crystal composition though it is not detected that the substance or material shows a liquid crystalline phase.
2. Description of the Related Art
As the display system using a liquid crystal display element, which is widely utilized in practice at present, there can be mentioned the twisted nematic type (TN type) and dynamic scattering type (DS type). In these display system, display is performed by a nematic liquid crystalline cell comprising a nematic liquid cell as the main component. One defect of the conventional nematic liquid cell is a low response speed, and only a response speed of several milliseconds is obtained. This defect is one cause of limitation of the application range of the nematic liquid cell. Recently, however, it has been found that a high response speed can be obtained if a smectic liquid crystalline cell is used.
It has been clarified that some optically active smectic liquid crystals have a ferroelectric property, and there are great expectation on the utilization of such liquid crystals. Liquid crystals having a ferroelectric property, that is, ferroelectric liquid crystals, are compounds synthesized by R. B. Meyer et al in 1975, which are represented by 2-methylbutyl 4-(4-n-decyloxybenzilydene-amino)cinnamate (hereinafter referred to as "DOBAMBC"). The compounds are characterized as exhibiting a ferroelectric property in the chiral smectic C phase (hereinafter referred to as "Sc * phase") [J. Physique, 36, L-69 (1975)].
N. A. Clark et al found that a high-response speed of an order of microseconds is obtained in a film cell of DOBAMBC [Appl. Phys. Lett., 36, 89 (1980)], and with this finding as a momentum, the ferroelectric crystal has attracted attention as a material applicable not only to a display system such as a liquid crystal television but also to an optical printer head, an optical Fourier converting element, a light valve, and other optoelectronic elements because of high-speed response characteristics.
Since DOBAMBC has a small spontaneous polarization and is a Schiff base, it has poor physical and chemical stabilities. Accordingly, various physically and chemically stable compounds have been investigated as ferroelectric liquid crystalline materials. At present, research work on the development of ferroelectric liquid crystalline materials is concentrated on an enhancement of the high-speed response characteristic, orientation effect, contrast characteristic, memory characteristic, and threshold value characteristic, and optimization of practical properties such as the temperature dependencies of these characteristics.
However, none of the known ferroelectric liquid crystals, when used alone, shows a large spontaneous polarization, a low viscosity, a long helical pitch, an appropriate molecular tilt angle and a continuous phase transition (V*.fwdarw.SA.fwdarw.Sc*) within a broad temperature range including room temperature such that the above-mentioned practically desired properties are manifested. Therefore, practically, attempts have been made to optimize the foregoing characteristics by mixing several compounds such as a compound having or inducing a large spontaneous polarization, a compound having a low viscosity and compounds having reverse helical pitches. The incorporation of a ferroelectric liquid crystal showing a ferroelectric characteristic within a broad temperature range or a smectic C liquid crystal (Sc) which is not chiral is effective for obtaining a liquid crystal composition showing a ferroelectric characteristic within a broad temperature range. A Sc is very important to obtain a liquid crystal composition within a broad temperature range, because a molecular structure of compound formed a Sc phase is a long helical pitch and it is able to comprise the Sc compound without a limitation of a volume in a liquid crystal composition. The research work on the development of a novel compound as a constituent of a liquid crystal composition, which has a performance of a high speed response and shows a Sc phase within a broad temperature range is worth to be carried out.
An optically active phenyl pyrimidine compound represented by following general formula (IV) which has a skeleton to be high speed response has carried out by Seiko Electric Industry Company and Teikoku Kagaku Co., Ltd. (The digest of 11th liquid crystal conference, 2N18, 2N19, 2N20, 2N21) EQU R.sub.7 --Ph--Py--R.sub.8 (VI)
wherein Ph represents 1,4-phenylene group, Py represents 2,5-pyrimidine group, R.sub.7 and R.sub.8 represent alkyl group, acyloxy group, alkoxy group or alkylcarbonyloxy group, either R.sub.7 or R.sub.8 represents an optically active branched group.
One of the defects of the compound is a small spontaneous polarization. But the compound has a good performance of a high speed response because of own low viscosity. Other defect of the compound has not a smectic phase because of having a branched group of the compound. The acknowledge carried out a component technique of a conventional TN type cell is no use on the compound. Further defect of the compound, it is difficult to settle constituent volume in a liquid crystal composition because of an optically active characterisity and an own helical pitch.
On the other hand, a phenyl pyrimidine Sc liquid crystal compound having linear alkyl group represented by following general formula (II) has already known. (H. Zaschke, R. Stolle, Z. Chem. 15, 441 (1975), Flussige Kristalle in Tabellen, Verlag Grundstoffind, Leipzig, 2nd ed. (1976))
Since a phase transition point (SA.fwdarw.Sc) of the compound is low, less than 70.degree. C., the compound is not suitable to use for constituent of a liquid crystal composition. EQU R.sub.3 --Ph--Py--R.sub.4 (II)
wherein Ph represents 1,4-phenylene group, Py represents 2,5-pyrimidine group, R.sub.3 and R.sub.4 represent independently linear alkyl group, linear acyloxy group or linear alkoxyl group. Either R.sub.3 or R.sub.4 represents linear alkyl group having more than seven carbon atoms.